Mine is definitely Code Geass or Seitokai no Ichizon.
I'm not sure why I enjoyed Code Geass so much though. I mean, I guess it's probably because of how good the ending was, but either way, it's definitely the best anime I've watched (In m opinion), though, Seitokai no Ichizon was probably my favorite. It's literally the funniest series I've ever watched, be it anime or else. I didn't go a minute without laughing in any episode. I'd definitely sugest watching it, if you haven't already. Super underrated.